FIG. 7 shows a tire T for motor vehicles which is generally known and which comprises a carcass 1 having beads 2 within the respective opposed ends along its inner periphery, a tread 4 provided over the outer periphery of the carcass 1 with a breaker 3 interposed therebetween, sidewalls 5 provided on opposite side faces of the carcass 1, and a breaker cushion 6 embedded between the carcass 1 and opposite each edge portion of the breaker 3. When the breaker 3 which is in the form of a hollow cylinder is adhered to the toroidal carcass 1 to form a green tire, a space or clearance occurs towards the edges of the breaker and the breaker cushions 6 are positioned on the carcass 1 to fill the space so the breaker 3 may have the desired cylindrical form.
FIG. 8 shows an example of an apparatus for building such a green tire. The apparatus comprises headstocks 8, 9 mounted on the respective ends of a base 7 and having a common horizontal axis, a belt drum 12 and a tire carcass building drum 13 which are both radially expandable and contractible and which are rotatably supported, each at one end, respectively by rotary shafts 10, 11 on the headstocks 8, 9. Belt transport means 14 are provided which can be moved between the two drums 12, 13. The tire carcass building drum 13 comprises a drum body composed of a plurality of drum segments divided circumferentially thereof, an annular inflatable shaping bladder 15 around the drum body, and inflatable side bladders 16 arranged on respective axially opposite sides of the forming bladder 15. The belt drum 12 is in the form of a hollow cylinder comprising a plurality of drum segments divided circumferentially thereof and radially expandable and contractible.
The process illustrated in the FIGS. 9 to 13 is already known as a process for building green tires. With reference to FIG. 9, a belt B comprising a breaker 3 and a tread 4 is formed using the apparatus shown in FIG. 8 as now follows. The breaker is wound in on one or a plurality of layers around the belt drum 12 in its radially expanded condition (FIG. 9 (I)). The tread 4 is wound around and adhered to the breaker 3 (FIG. 9 (II)) to form the belt B in the shape of a hollow cylinder. The drum 12 is then radially contracted, and the belt B is taken from the drum by means of the belt transport means 14, which is then placed in a stand-by position.
The tire carcass building drum 13 is radially contracted and then a tire carcass component material 1a is wound around the shaping bladder 15 and the side bladders 16 to form a cylindrical tube. A pair of beads 2 and a pair of breaker cushions 6 are fitted one to the tube in the positions shown in FIG. 10 (I). Next, as shown in FIG. 10 (II), the belt building drum 12 is slightly expanded to engage and lock the beads 2. The side bladders 16 are then inflated to fold the carcass material 1a around the beads 2, and the shaping bladder 15 is thereafter inflated to shape the carcass 1 into a toroidal shape as seen in FIG. 10 (III).
Subsequently, the waiting transport means 14 is moved to position the belt B around the outer periphery of the carcass 1 as shown in FIG. 11, the shaping bladder is then slightly inflated to fixedly position the belt B on the carcass 1 in the required position, and the transport means 14 is retracted. The forming bladder 15 is thereafter further inflated to intimately fit together the carcass 1, the breaker 3 and the breaker cushions 6 as seen in FIG. 12. As seen in FIG. 13, sidewalls 5 are adhered to the respective side faces of the carcass 1, and the shaping bladder 15 and the building drum 13 are contracted to allow removal of the completed green tire from the apparatus. The green tire thus formed is subjected to heat and pressure in a vulcanising press to bond the components together and mold the completed tire with its tread pattern.
With the conventional green tire assembly process described, the breaker cushions 6 are affixed to the carcass 1 in the form of a hollow cylinder, which is thereafter radially expanded to the final toroidal shape. This makes it extremely difficult to form the breaker cushions 6 of the required configuration in the finished tire. Also it is impossible to embed position the breaker 3 in the tire structure with its desired cylindrical shape with any real degree of accuracy. These difficulties lead to variations in the tire which have an adverse effect on tire uniformity and impair durability in service.